How to get file size in C++
Certainly! Here's a basic concept related to getting the file length in C++:
In C++, you could achieve the document size using the <fstream> header, which gives training and capabilities for operating with documents. The std::ifstream class is mainly beneficial for input record operations. The widespread steps involved are as follows:
- Include the <fstream> header at the beginning of your C++ document.
- Open the record for the use of an example of the std::ifstream class. Specify the report name and the opening flags std::ifstream::ate and std::ifstream::binary. The std::ifstream::ate flag positions the document pointer on the top of the file during the whole operation, and std::ifstream::binary ensures that the record is handled as a binary record (beneficial for non-text documents).
- Check if the document changed into efficiently opened. If the record cannot be opened, manage the mistake, as it should be primarily based on your application's necessities.
- Retrieve the record position by calling the tell () member characteristic at the std::ifstream object. The tell () function returns the current role of the record pointer. Since we located the pointer on the top of the record, the usage of std::ifstream::ate, the lower back value corresponds to the file size.
- Close the file by calling the near() member feature at the std::ifstream object. This step is crucial to release device sources and ensure the record is not locked.
- Use the received record size as needed. You can cast it to the suitable numeric type, carry out any favored calculations, or show it in a desired format.
- It's crucial to address errors during document operations to ensure that your software behaves efficaciously. Checking if the report became successfully opened and dealing with any ability mistakes is essential for vital record dealing.
By following these steps and using the correct features and lessons from the <fstream> header, you can easily retrieve the document size in C++ and incorporate it into your packages.
Program:
#include <iostream> #include <fstream> int main(){ // Step 1: Include the necessary headers // Step 2: Open the file using std::ifstream std::ifstream file("filename.ext", std::ifstream::ate | std::ifstream::binary); // Step 3: Check if the file was successfully opened if (!file.is_open()) { std::cerr<< "Error opening the file." << std::endl; return 1; // Exit the program indicating an error } // Step 4: Retrieve the file position std::streamposfileSize = file.tell(); // Step 5: Close the file file.close(); // Step 6: Use the fileSize variable std::cout<< "File size: " <<static_cast<double>(fileSize) << " bytes" << std::endl; return 0; // Exit the program indicating success }
Output:
Error opening the file.
Explanation:
Now let’s explain this program and provide an explanation for every step:
The important headers, <iostream> and <fstream>, are included at the beginning of this system. <iostream> is needed for general input/output, even as <fstream> is needed for file operations. In the main() characteristic, a file named "filename. ext" is opened using std::ifstream. The std::ifstream::ate flag positions the file pointer on the give up of the record at some stage in the whole operation, and ‘std::ifstream::binary’ guarantees that the report is dealt with as a binary file (valid for non-textual content documents).
The application assesses if the report successfully opened the usage of the is _open() member function of the std::ifstream object. If the file cannot be opened, an error message is printed to the usual blunders stream (‘std::carry), and the program returns with an error code of one.
The application retrieves the document role using the telling () member feature, which returns the modern-day position of the report pointer. Since we positioned the pointer at the cease of the record, using std::ifstream::ate, the again value corresponds to the scale of the file. The record is closed using the near() member feature of the std::ifstream object. Closing the record is crucial to launching device assets and ensuring the file is only sometimes locked.
Finally, the acquired document length is used. It is cast to double and displayed as the report size in bytes to the same old output (std::cout).
Remember to update "filename. ext" with the actual document course and name in the application. This software demonstrates a way to get the report length in C++ using the <fstream> header and affords designated reasons for each step.
Complexity Analysis:
The time and space complexities for the given code are as follows:
Time Complexity:
- Opening the file, the usage of std::ifstream: The time complexity of this operation depends on the underlying report gadget and the dimensions of the report name. It can be considered as O(1) or regular time complexity in maximum instances.
- Moving the record pointer to the end of the use of std::ifstream::ate: The time complexity of this operation is O(1) as it positions the file pointer directly on the quit of the file.
- Retrieving the record role the usage of std::ifstream::tellg: The time complexity of this operation is O(1) as it, without delay, returns the current role of the file pointer.
- Closing the report using std::ifstream::near: The time complexity of this operation is O(1) because it releases the report resources.
- Overall, the code's time complexity may be considered as O(1) or steady time complexity. It does no longer depend upon the dimensions of the file being processed.
Space Complexity:
- std::ifstream object: The space complexity for the std::ifstream object is O(1) because it occupies a hard and fast memory to keep the document records and the file pointer.
- Other variables: The space complexity for different variables, consisting of fileSize, is likewise O(1) as they occupy a set amount of reminiscence regardless of file size.
- Overall, the space complexity of the code is O(1) or consistent space complexity. The memory usage does not scale with the document's dimensions being processed.
Other methods to get file size:
There are several methods to obtain the file size in C++ besides the std::ifstream class and the fstream header. Here are a few methods to consider:
1. Using C-style File Operations:
C-style file operations can be used to determine the file size. Here's an illustration:
Program:
#include <iostream> #include <cstdio> int main() { FILE* file = std::fopen("filename.ext", "rb"); if (!file) { std::cerr<< "Error opening the file." << std::endl; return 1; // Exit the program indicating an error } std::fseek(file, 0, SEEK_END); long fileSize = std::ftell(file); std::fclose(file); std::cout<< "File size: " <<fileSize<< " bytes" << std::endl; return 0; // Exit the program indicating success }
Output:
Error opening the file.
Explanation:
- The vital headers, <iostream> and <cstdio>, are blanketed at the start of the code. The <iostream> is wanted for trendy input/output, at the same time as <cstdio> offers C-style document operations.
- The main() function starts offevolved; that's the access point of the program.
- A FILE* pointer named report is asserted to represent the report being opened. The std::fopen characteristic opens the record "filename. ext" with the mode "rb" for binary analysis. If the file cannot be opened, a mistakes message is outlined to the normal error circulation (std::cerr), and the program returns with a mistakes code of one.
- The std::fseek feature refers to moving the record pointer to the cease of the document. The characteristic takes 3 arguments: the report pointer, an offset (zero in this example to signify no offset), and the starting place position (in this situation, SEEK_END to are trying to find relative to the give up of the file).
- The std::ftell feature is used to retrieve the modern-day function of the report pointer. It returns a protracted fee representing the report length in bytes.
- The std::fclose function is called to close the file. This step is critical to launching machine sources.
- Finally, the file size is printed to the standard output (std::cout) alongside a descriptive message.
- The application ends with the aid of returning zero, indicating successful execution.
- This code demonstrates how to get the document size using C-style record operations. It opens the record, actions the document pointer to the cease, retrieves the report position (which represents the document length), closes the document, and displays the report length in bytes. The mistakes coping with ensure that appropriate messages are displayed in case of any disasters during report operations.
- Remember to replace "filename. ext" with the actual record path and call in the code.
Complexity Analysis:
The time and space complexity of the given code can be analyzed as follows:
Time Complexity:
- Opening the record with the use of std::fopen: The time complexity of this operation depends on the underlying document machine and the dimensions of the file name. In most cases, it may be considered O(1) or constant time complexity.
- Moving the file pointer, the usage of std::fseek: The time complexity of this operation is O(1) since it indeed updates the report pointer position.
- Retrieving the record role the use of std::ftell: The time complexity of this operation is O(1) as it directly returns the present-day role of the file pointer.
- Closing the record with the use of std::fclose: The time complexity of this operation is O(1) as it genuinely releases the report resources.
- Overall, the code's time complexity may be considered as O(1) or constant time complexity. It does no longer rely on the dimensions of the record being processed.
Space Complexity:
- FILE* pointer: The area complexity for the FILE* pointer is O(1) because it occupies a fixed quantity of memory to keep the file pointer.
- Other variables: The space complexity for other variables, which includes fileSize, is also O(1) as they occupy a hard and fast amount of memory regardless of the record length.
- Overall, the space complexity of the code is O(1) or consistent space complexity. The reminiscence utilization does not scale with the scale of the record being processed.
2. Using std::filesystem (C++17 or later):
#include <iostream> #include <filesystem> int main() { std::filesystem::path filePath("filename.ext"); if (!std::filesystem::exists(filePath)) { std::cerr<< "File does not exist." << std::endl; return 1; // Exit the program indicating an error } std::uintmax_tfileSize = std::filesystem::file_size(filePath); std::cout<< "File size: " <<fileSize<< " bytes" << std::endl; return 0; // Exit the program indicating success }
Output:
The file does not exist.
Explanation:
- The code begins with the aid of consisting of the essential headers <iostream> and <filesystem>. These headers offer the desired capabilities and classes for report size retrieval.
- The main() function is defined, which serves as the entry point of the program.
- Inside the main() function, a std::filesystem::direction object named filePath is created. This item represents the report for which we need to retrieve the size. It would help if you had to update the string "filename. ext" with the actual file route and call you must paint with.
- The code checks if the report exists the usage of the std::filesystem::exists() characteristic. This function takes the record route as an issue and returns a boolean cost indicating whether the record exists or is no longer. If the record does not exist, it approaches that the path is wrong or the record isn't always present. In one of these cases, the code displays a mistakes message to the usual mistakes flow the usage of std::cerr and returns with an error code of 1 to indicate that a blunder occurred.
- If the report exists, the code retrieves the document length and the usage of the std::filesystem::file_size() characteristic. This characteristic takes the report path as an issue and returns the reported scale in bytes as a std::uintmax_t value. The record length represents the whole range of bytes occupied by using the record on the storage device.
- The retrieved file size is stored in the fileSize variable of type std::uintmax_t.
- Finally, the file length is printed to the usual output using std::cout. The << operator concatenates the descriptive message "File length: " with the fileSize value, and the result is despatched to the usual output. The length is outlined in bytes. For example, if the report length is 1024 bytes, the output may be "File size: 1024 bytes".
- The application concludes by returning 0 from the main() function, indicating successful execution.
- This code utilizes the <filesystem> library, which was brought in C++17, to paintings with documents and directories. It provides a convenient and platform-impartial manner to retrieve file-length data.
Complexity Analysis:
The time and space complexity of the code for retrieving the document length using std::filesystem can be analyzed as follows:
Time Complexity:
Checking document existence with the std::filesystem::exists() function takes regular time as it checks the file’s metadata.
Retrieving the file length with the std::filesystem::file_size(), feature also takes constant time as it directly retrieves the scale records from the record's metadata.
Overall, the time complexity of the code is considered constant, or O(1), because it no longer relies upon the dimensions or content of the document. The operations performed are mostly metadata lookups, which are generally green and have a regular time complexity.
Space Complexity:
The space complexity of the code is likewise consistent, or O(1), as now it does not allocate additional reminiscence that grows with the scale of the entry. The best memory used is storing the record course in the filePath object and the file length within the fileSize variable. Both require a set quantity of memory, regardless of the file length.